Current amp vs Voltage amp

05-05-13: Unsound
Al, the wouldn't sensitivity of the speaker vary along with the impedance?

Sensitivity, defined as the sound pressure level (SPL) generated by the speaker at a given distance, in response to a given voltage at its input terminals, at a given frequency, is what it is for a given speaker.

If the impedance of the speaker varies widely as a function of frequency, and if the speaker is driven by a tube amplifier having significant output impedance, then the voltage that appears at the input terminals of the speaker, which will be essentially the same as the amplifier's OUTPUT voltage, will vary significantly as a function of frequency, for a given INPUT voltage to the amplifier.

If the same speaker is driven by a solid state amplifier having near zero output impedance, then the voltage that appears at the input terminals of the speaker will NOT vary significantly as a function of frequency, for a given INPUT voltage to the amplifier.

What matters is minimizing the variation of SPL, as a function of frequency, for a given INPUT voltage to the amplifier. Which of those two scenarios will produce the best results in that respect depends on the design of the particular speaker, and what kind of amplifier the designer envisioned it being used with.

Deadlyvj, thanks for providing the interesting link. A bottom line summary seems to me to be contained in this quote:

Due to voltage driving, the sonic performance of virtually all loudspeaker systems is severely impaired by the diverse electromotive forces (see above) induced in the voice coil motor corrupting the ideal behaviour of the amplifier interface....

The effect is not unknown and can be traced down, but Meriläinen strongly feels that the noise mechanisms related to traditional voltage driving have not been adequately addressed, not in the literature, nor in practice.

No amplifier can remove the internal EMF voltage components at the driver motor, but their diverse effects on the speaker/amplifier interface and hence, on the sound quality, can be diminished with a sufficiently high source impedance.

I think that commenting on that intelligently would require both study of the details that are contained in his book, and more knowledge of speaker design than I possess. But his thesis, as I see it, does not change the fact that if a speaker has wide variations of impedance as a function of frequency, it is likely to perform best with an amplifier having whatever kind of output impedance the designer envisioned it being used with.

Best regards,
-- Al

If we put aside the issue of damping for the moment, and so long as such a ss amplifier has the required output power, such a ss amplifier would almost always be able to provide more linear output regardless of whether they are ESL's or dynamic speakers, and that would hold true whether or not the impedance swings were wide or not. Whether or not thus would always be audible is of course another issue.:-)

Hi Unsound,

Yes, "such a ss amplifier would almost always be able to provide more linear output regardless of whether they are ESL's or dynamic speakers, and that would hold true whether or not the impedance swings were wide or not." (Assuming that by "linear" you are referring to flat frequency response).

However, as I indicated that is not what matters. What matters, with respect to this issue, is the frequency response flatness of the output of the SPEAKER, as judged against the INPUT to the AMPLIFIER. Which in turn depends on how suitable the match is between amplifier output impedance and the design of the particular speaker.

Frequency response flatness at the amplifier output/speaker input has no direct relevance. Speakers whose impedance varies significantly as a function of frequency, and that match most optimally with tube amps, can be presumed to require a non-flat frequency response at their input terminals to produce an acoustic output whose frequency response is flat. If such a speaker is mated with a solid state amplifier having near zero output impedance, frequency response flatness will have been optimized at the output of the amplifier, but it will be wrong at the output of the speaker.

Best regards,
-- Al

Please forgive me, as I don't seem to understand.
I would think that if the speakers impedance varies, and as such it's sensitivity varies, I would think that unless the amplifier can adapt its power output appropriately, the speakers frequency output response will deviate from linearity.

@ Almarg, Hi, I was currious of your statement above, amps operate in a current mode and voltage mode?,, This is quite confussing to me,, My Krell 700cx clearly on all the technical papers, says this amp solely operates only in the current domain!, Krell is very famous for doing that!,, If you can study up on these technical papers for me, that would be cool!How can Krell make such a statement?,, thanks Almarg!,, cheers!